1. Field of the Invention
Immunoassays provide a technique for measuring specific compounds by employing the properties of anti-bodies or other receptors, which recognize a specific polar and spatial organization of an antigen. In many instances, the antibodies and antigens are obtained as complex mixtures of proteins, where the compounds of interest may be present in minor amount and in some instances an extremely small proportion of the total proteins present.
The immunoassays depend upon the ability to label one of the members of the specific binding pair--antigen and homologous antibody--with a label which provides a detectible signal. The methods then provide for distinguishing between the amount of the labeled member of the specific binding pair bound to its reciprocal member and unbound labeled member.
In many assays, no separation is involved when distinguishing between bound and unbound labeled member. To the extent that the labeled member is accompanied with other labeled material, this additional label provides a background signal which reduces the sensitivity and accuracy of the assay. Even where a separation step is involved, in many instances, it will be useful to minimize the presence of contaminating labeled material.
It is therefore desirable to provide a method for obtaining reagents involving labeled members of specific binding pairs substantially free of other labeled material. Any such technique must not adversely affect the immunological properties of the reagent. In addition, the technique should allow for concentration and isolation of the desired material in a form useful for immunoassays.
2. Description of the Prior Art
U.S. Pat. Nos. 3,998,943 and 3,996,345 describe immunoassay techniques employing chromophores as labels for providing a detectible signal.